This competitive renewal will address a novel area of asthmatic disease that builds upon our previously funded grant and new preliminary data pertaining to the maintenance of chronic airway disease. In this proposal we will examine the role of stem cell factor (SCF) in the development of chronic allergic airway disease leading to overproduction of mucus and peribronchial remodeling through the overproduction of IL-17E (IL-25)-induced Th2 disease. Peribronchial leukocyte accumulation and activation is a major disease factor during development of asthmatic airway responses that leads to chronic airway disease. In particular, T cells and eosinophils have been reported to be the primary cells associated with induction of bronchial injury, and are thought to participate in bronchial obstruction, airway remodeling, and airway hyperreactivity. Our data provided for this application indicate that SCF is an eosinophil-activating factor that induces IL-25 production leading to increases in Th2 cytokine production in the airway via the activation of an IL-17RB+ (IL-25R) myeloid cell population. This proposal will examine how SCF production participates directly and indirectly in chronic allergen-induced IL-25-mediated Th2 responses through the activation and development of the bone marrow- derived myeloid cell population. Our hypothesis is that SCF expressed during allergen-induced responses is a key mediator for local production of IL-25 as well as the induction and accumulation of IL-25 responsive cell populations that contribute to the severity of the pathogenic responses, including Th2 cytokine production, mucus overexpression and airway remodeling. To test this postulate we will focus on mechanisms involved in the ability of pulmonary-derived SCF to induce Th2 cytokines and eosinophil related functions. Our studies will 1) establish that SCF contributes to the development of chronic airway disease and define its relationship to inflammation and Th2 cytokine production, 2) establish a role for SCF in IL-25 production in the airway, 3) determine what role pulmonary SCF production has during allergen responses on the development of IL-25 responsive T cells and myeloid cells in the lung and/or bone marrow, 4) identify whether the Th2 cytokine environment along with SCF is required for the development of the IL-25 responsive myeloid cell population, 4) determine whether inhibition of IL-25 reduces the development of long term chronic disease independent of SCF, and 5) identify IL-25 induced myeloid cells in naove animals. To assess the mechanisms of SCF-induced activation we will especially concentrate on those pertaining to differential SCF activation of local pulmonary and bone marrow associated cell populations. In addition, we will assess changes in normal, c-kit mutant, IL-25R-/- and 4get GFP/IL-4 reporter mice to elucidate the mechanism of SCF-induced activation during chronic disease development. Thus, these studies will clarify a number of previously unexplored questions in this novel area of research.